ones.
_Scuta_, apex pointed, with a very slight ridge running to the umbo;
basal margin equalling two thirds of the length of the terga, with an
internal basal rim; on the under side of each valve, beneath the umbo,
there is a strong tooth. Out of the numerous specimens, all excepting
one had their scuta unequally convex, with their occludent margins
unequally curved, that of the more convex valve at the umbo, curling
beyond the medial line. The basal end of the carina is, likewise,
slightly curved laterally, and always turns towards the more convex
valve. This inequality, as Mr. Gray pointed out to me, depends on the
position of the specimens; the flatter side lying close to the carapace
of the crab. _Terga_, flat, oblong, nearly rectangular; occludent margin
straight; basal angle, truncated, almost parallel to the occludent
margin; in width, three or four times as wide as the carina. _Carina_,
(fig. 1, _a_) short, narrow, slightly curved, upper part broadest, with
the apex rounded, only just passing up between the basal broad ends of
the terga; externally carinated, internally very slightly concave; basal
end abruptly truncated, crested, not deeply imbedded in the membrane of
the peduncle.

_Peduncle_, barely as long as the capitulum, apparently (for specimens
dry and much shrunk) narrow, surrounded by rings or folds of thicker
yellowish membrane, of which the upper ones retain moderately long
spines; low down these rings become confluent; whole surface finely
dotted, dots largest on the rings.

_Mouth._--Labrum highly bullate in the upper part, with a row of teeth
on the crest; mandibles with four teeth, the fourth close to the
inferior apex, which is very little developed, sometimes making the
fourth tooth appear simply bifid. Maxillae with two large spines on the
upper angle, beneath which there is a large depression, bearing one
rather long and thick, and four short and thick, spines; inferior
upraised part with a double row of longer and thinner spines.

_Cirri._--Posterior cirri with segments bearing five pairs of spines, of
which the lowest pair is very minute; intermediate spines minute; spines
of the dorsal tuft thin, of nearly equal size; segments not at all
protuberant, elongated. First cirrus, standing far separated from the
second (as in Scalpellum), with its nearly equal rami rather above half
as long as those of the second cirrus. Second cirrus with anterior ramus
not thicker, and scarcely more thick